ROME/MILAN, Dec 29 (Reuters) - Silvio Berlusconi said on Saturday that outgoing Prime Minister Mario Monti was plotting with the left in his centrist alliance’s bid to win Italy’s national election in February, but centrist leaders denied any secret accord.

Monti, who replaced Berlusconi as prime minister last year when Italy was scrambling to avert a financial crisis, said on Friday he wanted to unite a broad coalition of factions around a reform agenda aimed at easing the country’s economic woes.

Monti ended weeks of speculation when he confirmed his bid for a second term, pitting him against the centre-left Democratic Party (PD) and Berlusconi’s centre-right People of Freedom (PDL) party in a three-way contest.

Speaking to reporters at Milan Central railway station, Berlusconi said Monti wanted to help the left secure power after the Feb. 24-25 election so he could continue his austerity agenda of tax hikes and spending cuts.

“This grouping has been formed to favour the left - also the similarities with the left’s programme points in this direction,” he said, after earlier describing Monti as “the spare wheel” of the PD in an interview with Vista TV.

The 76-year-old billionaire, who caught the train from Rome with his 27-year-old partner, Francesca Pascale, said he did not believe Italian voters would “fall into the trap”, which he said was aimed at stealing votes from the centre right.

But Pier Ferdinando Casini, head of Italy’s oldest and largest centrist party, the UDC, which is cooperating with Monti, denied the accusations.

“Our initiative was not born with the support of the PD. It has not been started with a predetermined alliance ... until election day what’s important is aiming for the majority,” Casini said at a news conference on Saturday.

“PHASE OF RESPONSIBILITY”

Opinion polls suggest the PD, under Pier Luigi Bersani, will win a comfortable lower house majority but may have to strike a deal with centrist forces in the Senate, where the centre left has struggled to gain control in past elections.

The PD, which has pledged to maintain Monti’s broad reform course while putting more emphasis on jobs and growth, has urged the 69-year-old technocrat to clarify the approach the centrist forces will take towards the left.

“Will they present themselves as alternatives, as rivals, or as open to an alliance?” Bersani asked on SkyTG24 television on Friday, saying that the centre left would be open to discuss an accord when Monti’s position is clear.

Monti, a former European Commissioner, is a favourite with international investors, the Catholic Church and the business establishment, and has been widely credited with restoring Italy’s credibility after the scandal-plagued Berlusconi years.

“For the first time, an atmosphere is forming that points towards the future for a Europe that needs Italy and a country that wants to change deeply,” centrist leader Casini said on Saturday.

“As of yesterday, we are putting behind us the empty electoral promises, populism, demagoguery, fake assurances; a phase of responsibility is beginning,” he said.

Also on Saturday, Italian magistrate Antonio Ingroia officially announced he was joining the election race, and backers of his anti-corruption, law-and-order platform said it was time for both Monti and Berlusconi to step aside.

“We can’t give them back the keys to the country,” said Felice Belisario from the opposition Italy of Values party, which said it supported Ingroia’s candidacy for prime minister.

“Both have ruined Italy and have only acted in the interests of themselves and their friends at the expense of Italian citizens,” Belisario said in a statement.

The PD has so far maintained a tone of polite respect for Monti, in contrast to Berlusconi’s attacks on his “Germano-centric” austerity policies, which he blames for deepening a severe recession and fuelling record unemployment.

The media tycoon said on Saturday he was disappointed that Monti had made a bid for a second term because the economics professor had told him he would not use the exposure gained as an unelected technocrat for future political motives.

He said if the centre-right won the election he would launch an investigation into Monti’s ascent to power.

Later on Saturday Berlusconi met leaders of the Northern League, his former government allies. He told reporters following the meeting that he remained hopeful for a possible alliance but the PDL was still not convinced on some points.

PDL secretary Angelino Alfano said on Twitter that the disagreements could lead to the PDL and the Northern League heading their separate ways at the next election.